Scientists Link a Single Molecule to Why You Absolutely Must Scratch That Itch

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Scientists have begun unraveling how an itch is triggered and felt by the body. (Photo: Shutterstock.com)

The science of what causes an itch — not the stimulus per se but how the sense functions in the nervous system — has long fascinated and perplexed scientists.

Now, they’ve identified another piece in the puzzle as to what causes that nearly uncontrollable urge to scratch.

Researchers with the National Institutes of Health discovered a small molecule released in the spinal cord that eventually leads to the brain sensing an itch.

The discovery was made in mice studies where the nerve cell that is associated with the molecule, called natriuretic polypeptide b (Nppb), was removed.

When the nerve cell was absent from the mice, the scientists found they didn’t respond to a variety of stimuli that would generally trigger an itch/scratch response.

“When we exposed the Nppb-deficient mice to several itch-inducing substances, it was amazing to watch. Nothing happened. The mice wouldn’t scratch,” Santosh Mishra, lead author on the study, said in a statement.

The hope is that such findings would eventually lead to a treatment for patients with conditions that cause chronic itch. Removing the neurons, which would receive the molecule that would then send the itch-inducing sensation to the brain and cause the subject to want to scratch, didn’t impede any other sensory experiences, like feelings of temperature, pain, and touch, but the researchers did state that Nppb is also used by the heart, kidneys, and other parts.

Thus, controlling the neurotransmitter to prevent itch could easily lead to unintended side effects.

“Our work shows that itch, once thought to be a low-level form of pain, is a distinct sensation that is uniquely hardwired into the nervous system with the biochemical equivalent of its own dedicated land line to the brain,” Mark Hoon, Ph.D., the senior author on the paper, said in a statement.

“We have defined in the mouse the primary itch-initiating neurons and figured out the first three steps in the pruritic pathway,” Hoon said.

“Now the challenge is to find similar biocircuitry in people, evaluate what’s there, and identify unique molecules that can be targeted to turn off chronic itch without causing unwanted side effects. So, this is a start, not a finish,” he added.